This invention relates to improvements in gas filters and, more particularly, to a novel filter for the removal of selected oxidizable vapors from tobacco smoke.
It is often desirable to remove lower molecular weight aldehydes, such as acetaldehyde and acrolein, from gases without, at the same time, removing organic components containing double and triple bonds. There are numerous instances in laboratory and industrial applications wherein the selective removal of lower molecular weight aldehydes (and related compounds, such as corresponding alcohols, etc.) from gas streams while leaving the unsaturated hydrocarbon components thereof undisturbed is desirable. For example, in the free-radical catalyzed polymerization of ethlenically unsaturated monomers to produce high molecular weight polymers, traces of aldehyde and alcohol impurities in the feed stream interfere with the chain-propagating nature of the polymerization reaction. The consequence of such interference is the production of polymers having inferior properties, or the need to utilize larger quantities of relatively expensive catalyst.
Tobacco smoke, as produced by cigarettes, pipes, and cigars, is essentially an aerosol consisting of droplets and/or particles dispersed in a gaseous stream. The dispersed droplets and/or particles are generally referred to as the total particulate matter (TPM) of the smoke. The TPM can generally be removed in part from the smoke stream, if desired, by filtration devices attached to the smoking article which function to mechanically intercept and retain the suspended material. If complete removal of TPM is desired, as in analytical studies of the smoke, a standard Cambridge filter pad may be employed, which consists of a 1 mm thick circular matt of 45 mm diameter made of extremely fine diameter glass fibers. The portion of the smoke which passes through the Cambridge pad, under standard testing conditions, is referred to as the gas phase of the smoke.
Both the TPM and gas phase portions of tobacco smoke consist of a complex mixture of components which, collectively, produce the taste and aroma sensations sought and appreciated by those individuals who indulge in the smoking pastime. Some of the constituents of the smoke, however, do not have a beneficial effect on the subjectively perceived quality of the smoke and could be considered undesirable from a physiological standpoint. In this category are the low molecular weight aldehydes such as acetaldehyde and acrolein, which occur in small quantities in the gas phase of smoke derived from tobacco and cellulose-based tobacco substitutes.
A considerable amount of earlier work has been directed toward the removal of gas phase components from cigarette smoke. One general approach has been to provide a bed of granules of an active material in a compartment of a cigarette filter, through which the smoke passes. The most often mentioned active granular filter materials are silica gel and activated carbon. These materials, although capable of removing aldehyde compounds, are nonselective in their effect, and remove numerous other compounds considered necessary for acceptable flavor.